High performance CMOS devices comprising gapped dual stressors with dielectric gap fillers, and methods of fabricating the same

ABSTRACT

The present invention relates to complementary metal-oxide-semiconductor (CMOS) devices having gapped dual stressors with dielectric gap fillers. Specifically, each CMOS device of the present invention includes at least one n-channel field effect transistor (n-FET) and at least one p-channel field effect transistor (p-FET). A tensilely stressed dielectric layer overlays the n-FET, and a compressively stressed dielectric layer overlays the p-FET. A gap is located between the tensilely and compressively stressed dielectric layers and is filled with a dielectric filler material. In one specific embodiment of the present invention, both the tensilely and compressively stressed dielectric layers are covered by a layer of the dielectric filler material, which is essentially free of stress. In an alternatively embodiment of the present invention, the dielectric filler material is only present in the gap between the tensilely and compressively stressed dielectric layers.

FIELD OF THE INVENTION

This invention relates to high performance complementarymetal-oxide-semiconductor (CMOS) devices having gapped dual stressorstructures with dielectric gap fillers. More specifically, the presentinvention relates to CMOS devices each comprising at least one highperformance n-channel field effect transistor (n-FET) that is overlaidby a tensilely stressed dielectric layer and at least one highperformance p-channel field effect transistor (p-FET) that is overlaidby a compressively stressed dielectric layer, wherein a gap is locatedbetween the tensilely and compressively stressed dielectric layers andis filled with a dielectric filler material.

BACKGROUND OF THE INVENTION

Mechanical stresses within a semiconductor device substrate can be usedto modulate device performance. For example, in silicon, hole mobilityis enhanced when the film is under compressive stress, while theelectron mobility is enhanced when the silicon film is under tensilestress. Therefore, compressive and/or tensile stresses can beadvantageously created in the channel regions of a p-FET and/or an n-FETin order to enhance the performance of such devices.

However, the same stress component, either compressive or tensilestress, discriminatively affects the performance of a p-FET and ann-FET. In other words, compressive stress enhances the performance ofthe p-FET, but adversely impacts the performance of the n-FET, whiletensile stress enhances the performance of the n-FET, but adverselyimpacts the performance of the p-FET. Therefore, p-FET and n-FET requiredifferent types of stresses for performance enhancement, which imposes achallenge for concurrent fabrication of high performance p-FET and n-FETdevices, due to the difficulty in concurrently applying compressivestress to the p-FET and tensile stress to the n-FET.

One conventional approach for creating desired compressive and tensilestresses in channel regions of p-FET and n-FET devices is to cover thep-FET and the n-FET devices with compressively and tensilely stresseddielectric films, respectively, so that tensile and compressive stressescan be respectively applied to the n-FET and p-FET devices.

However, the tensilely and compressively stressed dielectric films inthe conventional CMOS devices are typically patterned by lithography andetching, which are prone to misalignments and may result in significantoverlay errors (e.g., in the range of about ±20 nm for the 45 nm nodedevices). Consequently, the tensilely stressed dielectric layer and thecompressively stressed dielectric layer cannot be perfectly aligned witheach other at their edges, and the boundary region where the tensilelyand compressive stressed dielectric layers meet typically containseither an overlap or a gap between these two layers.

FIG. 1A shows a top view of a conventional CMOS device that comprises ap-FET and an n-FET, and FIG. 1B shows a cross-sectional view of theconventional CMOS device through line A-A. Specifically, such aconventional CMOS device comprises a p-FET active region 102 and ann-FET active region 104 that are separated from each other by anisolation region 111. A common gate structure that comprises a patternedgate conductor 106 and a gate metal silicide layer 107 extend over bothactive regions 102 and 104 and across the isolation region 111. Gatedielectrics 122 and 142 respectively isolate the p-FET active region 102and the n-FET active region 104 from the patterned gate conductor 106.

On one hand, a compressively stressed silicon nitride layer 128selective overlays the p-FET active region 102, but not the n-FET activeregion 104. On the other hand, a tensilely stressed silicon nitridelayer 148 selectively overlays the n-FET active region 104, but not thep-FET active region 102. An optional etch stop layer 149, whichpreferably comprises a low temperature oxide (LTO), is provided over thetensilely stressed silicon nitride layer 148. As shown in FIG. 1B, thecompressively and tensilely stressed silicon nitride layers 128 and 148are not perfectly aligned at their edges but overlap significantly atthe boundary region 103. The misalignment between the compressively andtensilely stressed silicon nitride layers 128 and 148 may also form agap (not shown) at the boundary region 103.

In the incident that the tensilely and compressively stressed dielectriclayers overlap, as shown hereinabove in FIG. 1B, the boundary region hasa dielectric layer thickness that is twice of the thickness of thedielectric layer in other regions, which may cause insufficient contactetch. Specifically, if a metal contact is formed over the boundaryregion, such a metal contact may not be able to extend through the thickdielectric layer located on the boundary region and therefore fails tomake contact to the underlying FET components (e.g., the gate conductorsor the source/drain of the FETs).

In the alternative incident that a gap is formed between the tensilelyand compressively stressed dielectric layers, the etching process usedfor forming the metal contact opening through the tensilely orcompressively stressed dielectric layer may punch through the FETcomponents that are exposed through the gap between the tensilely andcompressively stressed dielectric layers. Further, the gap may allowsodium and other contaminants to diffuse into the exposed FET componentsand thereby causes degradation of the device performance.

SUMMARY OF THE INVENTION

The present invention advantageously overcomes the above-mentioneddrawbacks of the conventional CMOS device that comprises dual stressorlayers of tensile and compressive stresses, by first creating a gapbetween the tensile and compressive stressor layers and then filling thegap with a dielectric filler material. In this manner, any overlapbetween the tensilely and compressively stressed dielectric layers canbe effectively avoided, while the risk of contamination typicallyassociated with gapped dual stressor layers can be minimized orcompletely eliminated.

In one aspect, the present invention relates to a semiconductor devicecomprising:

-   -   at least one n-channel field effect transistor (n-FET) and at        least one p-channel field effect transistor (p-FET) that are        spaced apart from each other;    -   a tensilely stressed dielectric layer overlaying the at least        one n-FET; and    -   a compressively stressed dielectric layer overlaying the at        least one p-FET,    -   wherein a gap is located between the tensilely and compressively        stressed dielectric layers, and wherein said gap is filled with        a dielectric filler material that is different from the        tensilely and compressively stressed dielectric layers.

The dielectric filler material may differ from the tensilely andcompressively stressed dielectric layers in any physical orcompositional characteristic, such as, for example, density, etchingrate, stress, oxygen or nitrogen content, etc. Preferably, but notnecessarily, the dielectric filler material comprises different stressfrom the tensilely and compressively stressed dielectric layers. Morepreferably, the dielectric filler material is essentially free ofstress.

The gap preferably has a width ranging from about 1 nm to about 100 nm.More preferably, the gap width ranges from about 5 nm to about 80 nm,and most preferably from about 30 nm to about 50 nm.

In a specific embodiment of the present invention, the dielectric fillermaterial is essentially free of stress, and both the tensilely andcompressively stressed dielectric layers are covered by a layer of thedielectric filler material. In an alternative embodiment of the presentinvention, the dielectric filler material is present only in the gapbetween the tensilely and compressively stressed dielectric layers.

The tensilely and compressively stressed dielectric layers and thedielectric filler material may comprise any suitable dielectricmaterials with the corresponding stress profiles. Preferably, but notnecessarily, the tensilely stressed dielectric layer comprises tensilelystressed silicon nitride, the compressively stressed dielectric layercomprises compressively stressed silicon nitride, and the dielectricfiller material comprises silicon nitride that is different from suchtensilely and compressively silicon nitrides.

The n-FET and the p-FET as described hereinabove may comprise a commongate structure that is located under both the tensilely andcompressively stressed dielectric layers, or they may comprise separategate structures that are isolated from each other and are respectivelylocated under the tensilely and compressively stressed dielectriclayers.

In another aspect, the present invention relates to a method for forminga semiconductor device comprising:

-   -   forming at least one n-channel field effect transistor (n-FET)        and at least one p-channel field effect transistor (p-FET) that        are spaced apart from each other;    -   forming a tensilely stressed dielectric layer over both the        n-FET and the p-FET;    -   selectively removing a portion of the tensilely stressed        dielectric layer from the p-FET, wherein a remaining portion of        the tensilely stressed dielectric layer overlays the n-FET;    -   forming a compressively stressed dielectric layer over both the        n-FET and the p-FET;    -   selectively removing a portion of the compressively stressed        dielectric layer from the n-FET, wherein a remaining portion of        the compressively stressed dielectric layer overlays the p-FET,        and wherein a gap is located between the remaining portion of        the compressively stressed dielectric layer and the remaining        portion of the tensilely stressed dielectric layer; and    -   filling the gap with a dielectric filler material.

The dielectric filler material used for filling the gap in theabove-mentioned method can be either the same or different from thematerials contained by the tensilely and compressively stresseddielectric layers. Preferably, but not necessarily, the dielectricfiller material is different from the tensilely and compressivelystressed dielectric layers. More preferably, but not necessarily, thedielectric filler material comprises different stress from the tensilelyand compressively stressed dielectric layers.

Preferably, the gap is filled by depositing a layer of the dielectricfiller material over the tensilely and compressively stressed dielectriclayers and the gap therebetween, and the deposited layer of thedielectric filler material has a layer thickness that is larger thanhalf of the gap width.

In a still further aspect, the present invention relates to a method forforming a semiconductor device comprising:

-   -   forming at least one n-channel field effect transistor (n-FET)        and at least one p-channel field effect transistor (p-FET) that        are spaced apart from each other;    -   forming a compressively stressed dielectric layer over both the        n-FET and the p-FET;    -   selectively removing a portion of the compressively stressed        dielectric layer from the n-FET, wherein a remaining portion of        the compressively stressed dielectric layer overlays the p-FET;    -   forming a tensilely stressed dielectric layer over both the        n-FET and the p-FET;    -   selectively removing a portion of the tensilely stressed        dielectric layer from the p-FET, wherein a remaining portion of        the tensilely stressed dielectric layer overlays the n-FET, and        wherein a gap is located between the remaining portion of the        tensilely stressed dielectric layer and the remaining portion of        the compressively stressed dielectric layer; and    -   filling the gap with a dielectric filler material.

Other aspects, features and advantages of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view of a conventional CMOS device comprising an n-FETand a p-FET with significantly overlapped tensile and compressivestressor layers.

FIG. 1B is a cross-sectional view of the conventional CMOS device ofFIG. 1A along line A-A.

FIG. 2A is a top view of an improved CMOS device comprising an n-FET anda p-FET with a common gate structure and gapped tensile and compressivestressor layers, while a dielectric filler material layer that isessentially free of stress overlays both the tensile and compressivestressor layers and fills the gap therebetween, according to oneembodiment of the present invention.

FIG. 2B is a cross-sectional view of the improved CMOS device of FIG. 2Aalong line B-B.

FIG. 3A is a top view of an improved CMOS device comprising an n-FET anda p-FET with a common gate structure and gapped tensile and compressivestressor layers, while a dielectric filler material fills the gapbetween the tensile and compressive stressor layers, according to oneembodiment of the present invention.

FIG. 3B is a cross-sectional view of the improved CMOS device of FIG. 3Aalong line C-C.

FIG. 4A is a top view of an improved CMOS device comprising an n-FET anda p-FET with separate gate structures and gapped tensile and compressivestressor layers, while a dielectric filler material fills the gapbetween the tensile and compressive stressor layers, according to oneembodiment of the present invention.

FIG. 4B is a cross-sectional view of the improved CMOS device of FIG. 4Aalong line D-D.

FIGS. 5-10 are cross-sectional views that illustrate exemplaryprocessing steps for forming the improved CMOS device of FIGS. 2A-2B orFIGS. 3A-3B, according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present. It willalso be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

The term “essentially free of stress” as used herein refers to astructure or a material containing tensile or compressive stress that isless than about 400 MPa.

The present invention provides an improved CMOS device that comprises atleast one n-FET and at least one p-FET with dual stressor layers locatedthereon, i.e., a tensile stressor layer is located over the at least onen-FET and a compressive stressor layer is located over the at least onep-FET. A gap is first formed between the tensile and compressivestressor layers and is then filled with a dielectric filler material.Such a gap with dielectric filler material functions to avoid formationof any overlap between the tensilely and compressively stresseddielectric layers, while concurrently minimizing or completelyeliminating the risk of contamination typically associated with gappeddual stressor layers.

FIGS. 2A and 2B respectively show the top view and cross-sectional viewof an improved CMOS device, according to one embodiment of the presentinvention.

Specifically, the CMOS device comprises a p-FET that is located over ap-FET active region 2 and an n-FET that is located over an n-FET activeregion 4. The p-FET active region 2 and the n-FET active region 4 arelocated in the same semiconductor substrate (not shown) and areseparated from each other by an isolation region 11. A common gatestructure that comprises a patterned gate conductor 6 and a gate metalsilicide layer 7 extend over both active regions 2 and 4 and across theisolation region 11. Gate dielectrics 22 and 42 respectively isolate thep-FET active region 2 and the n-FET active region 4 from the patternedgate conductor 6.

A compressively stressed dielectric layer 28 selective overlays thep-FET active region 2, but not the n-FET active region 4, while atensilely stressed silicon nitride layer 48 selectively overlays then-FET active region 4, but not the p-FET active region 2. Optional etchstop layers 29 and 49 are respectively provided over the compressivelyand tensilely stressed dielectric layers 28 and 48.

The compressively and tensilely stressed dielectric layers 28 and 48 donot overlap in any manner. Instead, a gap 3 is present between thecompressively and tensilely stressed dielectric layers 28 and 48, asshown in FIG. 2B. A gap filler 52, which is formed of a dielectricfiller material, is provided in the gap 3 between the compressively andtensilely stressed dielectric layers 28 and 48. Because the n-FET andthe p-FET active regions 2 and 4 share a common gate structure acrossthe isolation region 11, the gap filler 52 is located directly over thecommon gate structure, instead of directly on the isolation region 11.

The dielectric filler material that forms the gap filler 52 may compriseany conformal dielectric material that can be used to fill the gap 3.Preferably, but not necessarily, the dielectric filler material isselected from the group consisting of oxides, nitrides, and oxynitrides.More preferably, the dielectric filler material comprises siliconnitride.

The dielectric filler material is deposited by a subsequent processafter formation of the tensilely and compressively stressed dielectriclayers 28 and 48. The dielectric filler material may differ from thetensilely and compressively stressed dielectric layers 28 and 48 in oneor more detectable physical or compositional characteristics such as,for example, density, etching rate, stress, and oxygen or nitrogencontent. Alternatively, the dielectric filler material can comprise thesame material as that contained by one of the tensilely andcompressively stressed dielectric layers 28 and 48, but it isdistinguishable from the tensilely or compressively stressed dielectriclayer 28 or 48 by an interfacial layer formed at the beginning of thesubsequent deposition process.

Preferably, but not necessarily, the dielectric filler materialcomprises either tensile or compressive stress that is quantitativelydifferent from that contained by the tensilely or compressively stresseddielectric layer 28 or 48. More preferably, the dielectric fillermaterial is essentially free of stress, i.e., it is stress-neutral.

In the specific embodiment shown by FIGS. 2A and 2B, the dielectricfiller material that forms the gap filler 52 also forms a layer 50 thatextends outside of the gap 3 to cover the compressively and tensilelystressed dielectric layers 28 and 48. In this specific embodiment, it isparticularly preferred that the dielectric filler material isstress-neutral, so that the layer 50 does not offset the desired stressprovided by the underlying stressor layers 28 and 48.

The gap 3 between the compressively and tensilely stressed dielectriclayers 28 and 48 preferably has a gap width that ranges from about 1 nmto about 100 nm, more preferably from about 5 nm to about 80 nm, andmost preferably from about 30 nm to about 50 nm.

Further, the dielectric filler material layer 50 preferably has a layerthickness that is more than half of the gap width. For example, when thegap width ranges from about 30 nm to about 50 nm, the layer thickness ofthe dielectric filler material layer 50 preferably ranges from about 20nm to about 30 nm.

Although FIGS. 2A and 2B shows a specific embodiment of the presentinvention in which excess dielectric filler material also forms a layer50 extending outside of the gap 3 to cover the compressively andtensilely stressed dielectric layers 28 and 48, the present inventionalso contemplates the alternative embodiment in which the excessdielectric filler material is removed from over the compressively andtensilely stressed dielectric layers 28 and 48, so that only the portionof the dielectric filler material that forms the gap filler 52 in thegap 3 remains in the final CMOS device.

FIGS. 3A and 3B therefore show the top view and cross-sectional view ofan improved CMOS device that is similar to that shown in FIGS. 2A and2B, except that the layer 50 formed of excess dielectric filler materialhas been removed from above the compressively and tensilely stresseddielectric layers 28 and 48.

Correspondingly, only a portion of the dielectric filler material thatforms the gap filler 52 is present in the gap 3 between thecompressively and tensilely stressed dielectric layers 28 and 48. Theoptional etch stop layers 29 and 49 located over the compressively andtensilely stressed dielectric layers 28 and 48 become exposed.Alternatively, if no etch stop layer is provided, the compressively andtensilely stressed dielectric layers 28 and 48 themselves will becomeexposed.

The n-FET and p-FET of the present invention may share a common gatestructure, as shown hereinabove by FIGS. 2A-3B, but they may alsocomprise separate gate structures that are isolated from each other.

FIGS. 4A and 4B show the top view and cross-sectional view of animproved CMOS device that is similar to that shown in FIGS. 3A and 3B,except that separate gate structures, one of which comprises a firstgate conductor 24 and a first gate metal silicide 25 and the other ofwhich comprises a second gate conductor 44 and a second gate metalsilicide 45, are provided over the p-FET active region 2 and the n-FETactive region 4, respectively. In this specific embodiment, the gapfiller 52 is no longer located over a common gate structure (as shownhereinabove in FIGS. 2A-3B), but is instead located directly on theisolation region 11, as shown in FIG. 4B.

The CMOS device structures as illustrated hereinabove can be readilyformed by well known lithographic, etching, and dielectric depositiontechniques. The CMOS devices can also be formed utilizing a conventionalreplacement gate process. Exemplary processing steps that can be usedfor forming the CMOS device structure of FIGS. 2A-2B or FIGS. 3A-3B willnow be described in greater detail by referring to the accompanyingdrawings in FIGS. 5-10. Note that in these drawings, which are not drawnto scale, like and/or corresponding elements are referred to by likereference numerals. It is further noted that in the drawings only onen-FET and one p-FET are shown. Although illustration is made to such anembodiment, the present invention is not limited to the formation of anyspecific number of n- and/or p-FET devices.

Reference is first made to FIG. 5, which shows formation of a blanketcompressively stressed dielectric layer 28 over a common gate structurethat comprises a patterned gate conductor 6 and a gate metal silicidelayer 7. The common gate structure is in turn located over a p-FETactive region 2 and an n-FET active region 4 that are located in thesame semiconductor substrate (not shown) and are isolated from eachother by the isolation region 11.

The semiconductor substrate (not shown), in which the p-FET activeregion 2 and the n-FET active region 4 are located, may comprise anysemiconductor material including, but not limited to: Si, SiC, SiGe,SiGeCi, Ge alloys, GaAs, InAs, InP, as well as other III-V or II-VIcompound semiconductors. The semiconductor substrate (not shown) mayalso comprise an organic semiconductor or a layered semiconductor suchas Si/SiGe, a silicon-on-insulator (SOI) or a SiGe-on-insulator (SGOI).In some embodiments of the present invention, it is preferred that thesemiconductor substrate (not shown) be composed of a Si-containingsemiconductor material, i.e., a semiconductor material that includessilicon. The semiconductor substrate (not shown) may be doped, undopedor contain doped and undoped regions therein. The p-FET active region 2may be formed of a first doped (n- or p-) region in the semiconductorsubstrate (not shown), while the n-FET active region 4 may be formed ofa second doped (n- or p-) region. Further, the p-FET and n-FET activeregions 2 and 4 may have the same or different conductivities and/ordoping concentrations.

The isolation region 11 is typically formed into the semiconductorsubstrate (not shown) to provide isolation between the p-FET and n-FETactive regions 2 and 4. The isolation region 11 may be a trenchisolation region or a field oxide isolation region. The trench isolationregion is formed utilizing a conventional trench isolation process wellknown to those skilled in the art. For example, lithography, etching andfilling of the trench with a trench dielectric may be used in formingthe trench isolation region. Optionally, a liner may be formed in thetrench prior to trench fill, a densification step may be performed afterthe trench fill and a planarization process may follow the trench fillas well. The field oxide may be formed utilizing a so-called localoxidation of silicon process.

After forming the at least one isolation region 11 within thesemiconductor substrate (not shown), a blanket gate dielectric layer(not shown) may be deposited over the entire surface of thesemiconductor structure (not shown). Alternatively, patterned gatedielectric layers 22 and 42 are formed respectively over the p-FETactive region 2 and the n-FET active region 4, as shown in FIG. 5. Thegate dielectric layers 22 and 42 can be formed by a thermal growingprocess such as, for example, oxidation, nitridation or oxynitridation.Alternatively, the gate dielectric layers 22 and 42 can be formed by adeposition process such as, for example, chemical vapor deposition(CVD), plasma-assisted CVD, atomic layer deposition (ALD), evaporation,reactive sputtering, chemical solution deposition and other likedeposition processes. The gate dielectric layers 22 and 42 may also beformed utilizing any combination of the above processes.

The gate dielectric layers 22 and 42 may be comprised of any suitableinsulating material, which includes, but is not limited to: an oxide,nitride, oxynitride and/or silicate including metal silicates andnitrided metal silicates. In one embodiment, it is preferred that thegate dielectric layers 22 and 42 are comprised of an oxide such as, forexample, SiO₂, HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, andmixtures thereof.

The physical thickness of the gate dielectric layers 22 and 42 may vary,but typically, the gate dielectric layers 22 and 42 each has a thicknessfrom about 0.5 to about 10 nm, with a thickness from about 0.5 to about3 nm being more typical.

After forming the gate dielectric layers 22 and 42, a common gateconductor 6, which preferably comprises polysilicon, is formed over boththe n-FET and p-FET active regions 2 and 4 and across the isolationregion 11, utilizing a known deposition process such as, for example,physical vapor deposition, CVD or evaporation, followed by a known gatepatterning process, such as lithography and etching. The common gateconductor 6 may be doped or undoped. If doped, an in-situ dopingdeposition process may be employed in forming the same. Alternatively, adoped polysilicon gate conductor 6 can be formed by deposition, ionimplantation and annealing. The thickness, i.e., height, of the commongate conductor 6 may vary depending on the deposition process employed.Typically, the common gate conductor 6 has a vertical thickness fromabout 20 to about 180 nm, with a thickness from about 40 to about 150 nmbeing more typical.

Optionally, but not necessarily, a metal silicide layer 7 is formed overthe gate conductor 6 by a known salicidation process, which is notdescribed in detail here in order to avoid obscure the presentinvention.

The gate conductor 6 and the optional gate metal silicide layer 7jointly form a common gate structure that extends over both the p-FETand n-FET active regions 2 and 4 and across the isolation region 11. Thecommon gate structure may comprise additional structures, e.g., sidewallspacers, cap layers and/or diffusion barrier layers (not shown), ascommonly included in MOS gate structures. In a preferred embodiment ofthe present invention, no sidewall spacer is present in the gatestructure, so that the device footprint can be reduced and the distancebetween adjacent device regions can be increased to facilitate thesubsequent gap filling.

After formation of the common gate structure, a compressively stresseddielectric layer 28, which preferably, but not necessarily, comprisescompressively stressed silicon nitride, is deposited over the entirestructure to cover both the p-FET active region 2 and the n-FET activeregion 4. The compressively stressed silicon nitride layer 28 can beformed by, for example, a plasma enhanced chemical vapor deposition(PECVD) process, as disclosed by U.S. Patent Application Publication No.2003/0040158 or by A. Tarraf et al., “Stress Investigation of PECVDDielectric Layers for Advanced Optical MEMS,” J. MICROMECH. MICROENG.,Vol. 14, pp. 317-323 (2004), or by any other suitable depositiontechniques well known in the art. Preferably, the compressively stressedsilicon nitride layer 28 has a thickness ranging from about 10 nm toabout 1000 nm, more preferably from about 20 nm to about 500 nm, andmost preferably from about 30 nm to about 150 nm.

An optional etch stop layer 29, which preferably, but not necessarily,comprises a low temperature oxide (LTO), can then be formed over thecompressively stressed dielectric layer 28. The LTO etch stop layer 29may be formed by a known low temperature oxidation process that istypically carried out at a processing temperature ranging from about300° C. to about 450° C.

Subsequently, a first block mask 60 is deposited over the compressivelystressed dielectric layer 28 and the optional etch stop layer 29 tocover only the portions of such layers that are located directly abovethe p-FET active region 2, while the remaining portions of layers 28 and29 located above the n-FET active region 4 are exposed, as shown in FIG.6.

A first selective etching step is then carried out using the first blockmask 60 to selectively remove the exposed portions of layers 28 and 29from above the n-FET active region 4, as shown in FIG. 7. One or moredry etching techniques, which include, but are not limited to: reactiveion etching (RIE), ion beam etching, plasma etching or laser ablation,can be used to selectively removed the exposed portions of layers 28 and29. The first block mask 60 is removed after the first selective etchingstep has been completed.

Next, a tensilely stressed dielectric layer 48, which preferably, butnot necessarily, comprises tensilely stressed silicon nitride, isdeposited over the entire structure to cover both the p-FET activeregion 2 and the n-FET active region 4. The tensilely stresseddielectric layer 48 specifically overlays the un-removed portions of thecompressive stressor layer 28 and the etch stop layer 29, as shown inFIG. 8. The tensilely stressed silicon nitride layer 48 can also beformed by the plasma enhanced chemical vapor deposition (PECVD) processdisclosed by U.S. Patent Application Publication No. 2003/0040158 or byA. Tarraf et al., “Stress Investigation of PECVD Dielectric Layers forAdvanced Optical MEMS,” J. MICROMECH. MICROENG., Vol. 14, pp. 317-323(2004), or by any other suitable deposition techniques well known in theart. Preferably, the tensilely stressed silicon nitride layer 48 has athickness ranging from about 10 nm to about 1000 nm, more preferablyfrom about 20 nm to about 500 nm, and most preferably from about 30 nmto about 150 nm. An optional etch stop layer 49, which preferably, butnot necessarily, comprises a LTO, can also be formed over the tensilelystressed dielectric layer 48.

A second block mask 62 is deposited over the tensilely stresseddielectric layer 48 and the optional etch stop layer 49 to cover onlythe portions of such layers that are located directly above the n-FETactive region 4, while the remaining portions of layers 48 and 49located above the p-FET active region 2 are exposed, as shown in FIG. 9.

More importantly, the second block mask 62 are constructed and arrangedso that it does not overlap with the un-removed portions of thecompressive stressor layer 28 and the etch stop layer 29, as shown inFIG. 9. Instead, the second block mask 62 is laterally offset from theun-removed portions of the compressive stressor layer 28 and the etchstop layer 29 by a significantly distance. In this manner, a secondselective etching step can be carried out to remove un-masked portionsof the tensilely stressed dielectric layer 48 and the optional etch stoplayer 49 from above the p-FET active region 2 and form a gap 3 betweenthe remaining portions of the tensilely stressed dielectric layer 48 andthe compressively stressed dielectric layer 28, as shown in FIG. 10.

After the second selective etching step, the second block mask 62 isremoved from above the n-FET active region 4, and a layer of adielectric filler material 50 is deposited over the entire structure.The dielectric filler material layer 50 not only covers thecompressively stressed dielectric layer 28 and the tensilely stresseddielectric layer 48, but also forms a gap filler 52 in the gap 3 betweenthe compressively stressed dielectric layer 28 and the tensilelystressed dielectric layer 48, as shown in FIG. 2B.

Further, an etch-back step can be carried out to remove excessdielectric filler material from above the compressively stresseddielectric layer 28 and the tensilely stressed dielectric layer 48,while leaving only the gap filler 52 in the gap 3 between thecompressively stressed dielectric layer 28 and the tensilely stresseddielectric layer 48, as shown in FIG. 3B. The etch-back step can also beterminated prematurely, so as to leave a significantly thinneddielectric filler material layer (not shown) over the compressivelystressed dielectric layer 28 and the tensilely stressed dielectric layer48.

Subsequently, conventional back-end-of-line processing steps, which arenot described herein in detail, can be carried out to form a completeCMOS device containing both a p-FET and an n-FET.

It should be noted that although the above-described processing stepsillustrate formation and patterning of the compressively stresseddielectric layer 28 before the tensilely stressed dielectric layer 48,the present invention is not limited to such a specific order. In otherwords, the tensilely stressed dielectric layer 48 can be readily formedand patterned before deposition and patterning of the compressivelystressed dielectric layer 28 in the practice of the present invention.

While the invention has been described herein with reference to specificembodiments, features and aspects, it will be recognized that theinvention is not thus limited, but rather extends in utility to othermodifications, variations, applications, and embodiments, andaccordingly all such other modifications, variations, applications, andembodiments are to be regarded as being within the spirit and scope ofthe invention.

1. A semiconductor device comprising: at least one n-channel fieldeffect transistor (n-FET) and at least one p-channel field effecttransistor (p-FET) that are spaced apart from each other; a tensilelystressed dielectric layer overlaying the at least one n-FET; acompressively stressed dielectric layer overlaying the at least onep-FET, wherein a gap is located between the tensilely and compressivelystressed dielectric layers, and wherein said gap is filled with adielectric filler material that is different from the tensilely andcompressively stressed dielectric layers.
 2. The semiconductor device ofclaim 1, wherein the dielectric filler material comprises differentstress from the tensilely and compressively stressed dielectric layers.3. The semiconductor device of claim 1, wherein the gap has a widthranging from about 1 nm to about 100 nm.
 4. The semiconductor device ofclaim 3, wherein the dielectric filler material is essentially free ofstress, and wherein both the tensilely and compressively stresseddielectric layers are covered by a layer of the dielectric fillermaterial.
 5. The semiconductor device of claim 3, wherein the dielectricfiller material is present only in the gap between the tensilely andcompressively stressed dielectric layers.
 6. The semiconductor device ofclaim 1, wherein the n-FET and the p-FET comprise a common gatestructure that is located under both the tensilely and compressedstressed dielectric layers.
 7. The semiconductor device of claim 1,wherein the n-FET and the p-FET comprise separate gate structures thatare isolated from each other and are respectively located under thetensilely and compressively stressed dielectric layers.
 8. A method forforming a semiconductor device comprising: forming at least onen-channel field effect transistor (n-FET) and at least one p-channelfield effect transistor (p-FET) that are spaced apart from each other;forming a tensilely stressed dielectric layer over both the n-FET andthe p-FET; selectively removing a portion of the tensilely stresseddielectric layer from the p-FET, wherein a remaining portion of thetensilely stressed dielectric layer overlays the n-FET; forming acompressively stressed dielectric layer over both the n-FET and thep-FET; selectively removing a portion of the compressively stresseddielectric layer from the n-FET, wherein a remaining portion of thecompressively stressed dielectric layer overlays the p-FET, and whereina gap is located between the remaining portion of the compressivelystressed dielectric layer and the remaining portion of the tensilelystressed dielectric layer; and filling the gap with a dielectric fillermaterial.
 9. The method of claim 8, wherein the dielectric fillermaterial is different from the tensilely and compressively stresseddielectric layers.
 10. The method of claim 8, wherein the dielectricfiller material comprises different stress from the tensilely andcompressively stressed dielectric layers.
 11. The method of claim 8,wherein the gap has a width ranging from about 1 nm to about 100 nm. 12.The method of claim 11, wherein the gap is filled by depositing a layerof the dielectric filler material over the tensilely and compressivelystressed dielectric layers and the gap therebetween, and wherein thedeposited layer of the dielectric filler material has a layer thicknessthat is larger than half of the gap width.
 13. The method of claim 12,further comprising removing excess dielectric filler material from overthe tensilely and compressively stressed dielectric layers, so that thedielectric filler material is only present in the gap between thetensilely and compressively stressed dielectric layers.
 14. A method forforming a semiconductor device comprising: forming at least onen-channel field effect transistor (n-FET) and at least one p-channelfield effect transistor (p-FET) that are spaced apart from each other;forming a compressively stressed dielectric layer over both the n-FETand the p-FET; selectively removing a portion of the compressivelystressed dielectric layer from the n-FET, wherein a remaining portion ofthe compressively stressed dielectric layer overlays the p-FET; forminga tensilely stressed dielectric layer over both the n-FET and the p-FET;selectively removing a portion of the tensilely stressed dielectriclayer from the p-FET, wherein a remaining portion of the tensilelystressed dielectric layer overlays the n-FET, and wherein a gap islocated between the remaining portion of the tensilely stresseddielectric layer and the remaining portion of the compressively stresseddielectric layer; and filling the gap with a dielectric filler material.15. The method of claim 14, wherein the dielectric filler material isdifferent from the tensilely and compressively stressed dielectriclayers.
 16. The method of claim 14, wherein the dielectric fillermaterial comprises different stress from the tensilely and compressivelystressed dielectric layers.
 17. The method of claim 14, wherein the gaphas a width ranging from about 1 nm to about 100 nm.
 18. The method ofclaim 17, wherein the gap is filled by depositing a layer of thedielectric gap material over the tensilely and compressively stresseddielectric layers and the gap therebetween, and wherein the depositedlayer of the dielectric filler material has a layer thickness that islarger than half of the gap width.
 19. The method of claim 18, furthercomprising removing excess dielectric filler material from over thetensilely and compressively stressed dielectric layers, so that thedielectric filler material is only present in the gap between thetensilely and compressively stressed dielectric layers.